Questions And Answers

The worksurface used is conductive (stainless steel) and sit on a conductive floor with Megohms resistance. The test equipment (test fixture + computer system) is placed on the metal surface for product testing. However, the Technician’s feedback is that they can feel the static charge through the metal table while performing the tests. One table has two test equipment [setups] sitting side by side. Somehow only one test equipment [setup is] having this problem. We have used the staticfield meter to check the static charge on the PC and the fixture used. They all meet our internal requirement (<200 volts). The root cause of the problem still cannot be found. - Goh Mei Li, MCMS Sdn Bhd, Penang, Malaysia

Answer

Right off the bat, this sounds like a grounding problem. Make sure that the test equipment setup that is causing the problem is properly wired to the AC power, especially including it’s ground connection. Have an electrician check this for you.Another thought is that the operator, if not grounded via wrist strap or foot strap, could be generating enough charge to discharge into the metal bench without any intervention from the test equipment. Lastly, the use of a metal (SS) bench top will easily cause ESD Events because there is essentially no resistance at this surface. If you were to cover the bench top with a dissipative grounded mat, such as Statfree T2™ matting material.